In urodynamic studies, the sacral reflex latency is used to examine certain spinal cord segments by stimulation of the pudendal nerve. The basic reflex arc from the glans penis or clitoris to the external urethral sphincter is believed to be from sensory fibers in the pudendal nerve to sacral cord internuncial neurons to motor fibers in the pelvic splanchnic nerve to skeletal muscle fibers in the external urethral sphincter. It has been suggested that the sacral reflex closely resembles the blink and other flexor reflexes derived from cutaneous receptors.
The sacral reflex has traditionally been obtained by use of electromyographic recording electrodes and electrical stimulation of the pudendal nerve. A bipolar electrode is applied to the glans penis or clitoris, followed by delivery of periodic electrical stimuli at gradually increasing intensities until a consistent reflex of the shortest latency is sensed via a monopolar needle electrode in the external urethra sphincter. As the electrical stimuli are administered, the responses are stored on the screen of the electromyograph for measurement and evaluation.
Due to the sensitivity of the area being stimulated, it will be appreciated that electrical stimulation to evoke this reflex can be quite uncomfortable for many patients, especially children, and can make it difficult or impossible to detect the reflex in patients with low pain thresholds. The apprehension, pain and discomfort actually can make the components of a flexor reflex more difficult to obtain. Further, stimulus artifact may occur when the electrical technique is used which can create problems in obtaining the sacral reflex, especially in women and children. Although mechanical stimulation has been applied previously in connection with evaluation of other physiocological responses, the technique of mechanical stimulation has not been used heretofor in determining sacral reflex latencies.
A need has thus arisen for an improved non-electrical method and apparatus for stimulating the pudendal nerve to determine sacral reflex latencies without the apprehension, pain and discomfort associated with the prior techniques.